The present invention relates to devices and methods for measuring the carbon activity of fluids containing carbon. It has particular application in the measurement of carbon activity in liquid metals such as sodium used as coolant in nuclear reactors or other systems.
The carburization and decarburization of stainless steels in contact with high-temperature liquid metals such as sodium can produce detrimental effects on mechanical properties. Therefore the determination of carbon activity within liquid-metal coolant of reactor systems can play an important role in determining the useful life of the reactor components.
Various methods have previously been employed to determine carbon content or carbon activity of a liquid-metal system. Some have involved the analysis of samples, either of the liquid metal itself or of solid metallic tabs exposed to the liquid metal. For more or less continuous monitoring, sampling techniques of this type require the frequent taking of samples and the required in-laboratory analysis which can be tedious and time-consuming.
Various meters for installation within lines or vessels containing liquid metal have included types that are based on the measurement of carbon diffusion rate through a metallic barrier. Since such meters require a flow of carbon out of the molten metal to be monitored, the measurement is influenced by the liquid-metal flow rate and by the form of dissolved carbon in the liquid metal. Thus, a simple measurement of the carbon activity is not obtained. Other systems involving electrochemical and pressure measurements have been quite complicated and have required precise and frequent calibration for accurate results. Impurities within the operating materials of such systems have produced additional difficulties in calibration and the selection of suitable range.